yes the w58 does mate to the 1jz, and like gareth says a mk3 w58 will require the jz bell housing for sure so your better off getting the mk4 one, slightly better internals, newer and is straight fit.
as for the r154 ma70/7mgte one, yes you only need the bell housing but theres a shit load of modding to be done on selector shaft and housing and rear mounting as they are different too! not forgetting its length which is smaller so youll need a modded propshaft too!
FYI theres 8 mounting holes in the jz flywheel and six on the 7mgte one so be carefull what you buy, although the splines are same on gearbox unlike the tt 2jz which have less splines and are bigger so flywheel has to be from 1jz too not 7mgte unless you mod the mk4 w58[n/a] flywheel by moving the lugs and use the 7mgte clutch, still theres quite a decent range of clutches out there since i did my conversion which should be adequate for the n/a push system, which means you could run the r154 box with jz bell housing,on w58 flywheel and uprated clutch no probs, but still the pull system is loads better for the torque of these motors.
IMHO keep the getrag unless youve got plenty of time, money and Ibuprofen